Scanned images may have a black line along the crease between the merged pages when scanning an A1 or A2 folded paper to combine the front and back images, using fi-7460, fi-7480, fi-7600, fi-7700, or fi-7700S.

This may be caused due to document inclination.
To reduce the amount of the black line, hold lightly the right and left edges of the paper like fig. 1 or 2 to ensure the paper is scanned without inclination.

Note:
Keep holding the document while the paper is fed. Do not hold the paper with too much force; otherwise it may results in paper jam.